Electrooptic intensity and phase modulators utilizing bulk inorganic crystals are well-known and widely utilized. Waveguide electrooptic modulators are a more recent development, and are described in literature such as Applied Physics Letters, 21, No. 7, 325 (1972); 22, No. 10, 540 (1973); and U.S. Pat. Nos. 3,586,872; 3,619,795; 3,624,406; 3,806,223; 3,810,688; 3,874,782; 3,923,374; 3,947,087; 3,990,775; and references cited therein.
One of the principal advantages of an optical waveguide configuration as contrasted to bulk crystals is that much lower electrical potentials and powers may be used with the optical waveguide configuration, and faster modulation rates also may be realized. Both of these operative characteristics are necessary to achieve high speed operation of such electrooptic modulators.
A thin film waveguide electrooptic modulator can operate employing one of several modulating mechanisms, e.g., linear phase modulation, Mach-Zehnder interferometry, directional coupling, Y junction, cross-bar switching, or rotation of the optical polarization.
The linear guided-wave type phase modulator is a well-known optical device which has been described in the literature. The phase modulator consists of a single waveguide of an electrooptically responsive medium, which have one or more pairs of electrodes positioned in proximity to the waveguiding medium. Information can be imposed on a transmitting optical beam in the form of phase shifts. Such phase shifts are effected by means of the positioned electrodes. When a voltage is applied to an electrode pair, the electrooptic effect changes the refractive index of the proximate waveguide zone changing the optical path length, thereby effecting a phase change in a waveguided light beam. Variations in applied voltage thus are transformed into the phase changes. The phase changes can be transformed into amplitude variations in the light output power level, by utilization of optical interferometry with a diverted portion of the incident light beam which travels through free space or by utilization of a homodyne detection technique.
There are other factors of critical concern in the design and fabrication of optical waveguides. The polarization properties of integrated optical switches and modulators are of great importance in determining the utility of these devices in an optical data tranfer system employing fiber transmission lines. In particular, these devices must perform efficient and complete switching of light, without regard to its state of polarization. This requirement arises because linearly polarized light coupled into single-mode circular fibers suffers a rapid conversion to other polarization states. Light coupled from a fiber therefore usually possesses an unknown elliptical polarization, and both transverse electric (TE) and transverse magnetic (TM) modes will be excited in the integrated optical circuit.
Polarization-independent optical switches and modulators are described in U.S. Pat. Nos. 4,243,295; 4,291,939; 4,514,046; 4,674,839; and references cited therein. The known polarization-independent waveguide devices all are constructed with inorganic waveguide channels such as crystalline LiNbO.sub.3, LiTaO.sub.3, GaAs or CdSe.
For a low voltage operating electrooptic modulator, highly responsive electrooptical media are required. LiNbO.sub.3 has been an important inorganic species for waveguide electrooptic modulator construction. However, there are certain inherent disadvantages in the use of LiNbO.sub.3 or other inorganic crystal in an electrooptic modulator, such as the limitation of the input optical power and operational wavelength due to the inherent photorefractive effect.
It is known that organic and polymeric materials with large delocalized .pi.-electron systems can exhibit electrooptic and nonlinear optical response, which in many cases is a much larger response than by inorganic substrates.
In addition, the properties of organic and polymeric materials can be varied to optimize other desirable properties, such as mechanical and thermoxidative stability and high laser damage threshold, with preservation of the electronic interactions responsible for nonlinear optical effects.
Of particular importance for conjugated organic systems is the fact that the origin of the nonlinear effects is the polarization of the .pi.-electron cloud as opposed to displacement or rearrangement of nuclear coordinates found in inorganic materials.
Nonlinear optical properties of organic and polymeric materials was the subject of a symposium sponsored by the ACS division of Polymer Chemistry at the 18the meeting of the American Chemical Society, September 1982. Papers presented at the meeting are published in ACS Symposium Series 233, American Chemical Society, Washington D.C. 1983.
Organic nonlinear optical medium in the form of transparent thin substrates are described in U.S. Pat. Nos. 4,536,450; 4,605,869; 4,607,095; 4,615,962; and 4,624,872.
The above recited publications are incorporated herein by reference.
There is continuing research effort to develop new nonlinear optical organic media and electrooptic devices adapted for laser modulation, information control in optical circuitry, and the like. The potential utility of organic materials with large second order and third order nonlinearities for very high frequency application contrasts with the bandwidth limitations of conventional inorganic electrooptic materials.
Accordingly, it is an object of this invention to provide a novel electrooptic modulator.
It is another object of this invention to provide a linear electrooptical phase modulator which contains an organic nonlinear optical component.
It is a further object of this invention to provide a polarization-insensitive polymeric thin film waveguide electrooptic phase modulator.
Other objects and advantages of the present invention shall become apparent from the accompanying description and drawing.